Metal working apparatus and process

ABSTRACT

This invention relates generally to the application of electromechanical transducer energy to a workpiece, and particularly to the utilization of a high Q electromechanical transducer capable of delivering extremely high-power outputs to a work surface for the deformation of metallic or non-metallic materials, such as, in riveting, cold heading, bonding, and swaging.

United States Patent 1191 McMaster et a1.

[ 1 July 24, 1973 METAL WORKING APPARATUS AND 3,224,086 12/1965 Balamuth et a1 227/131 PROCESS 3,267,780 8/1966 R0111 72/56 3,360,972 1/1968 Schwinghamer 72/56 [75] Inventors: Robert C- McMaster; Charles C. 3,475,628 /1969 McMastcr 0181 72/56 Libby, both of Columbus; Hildegard 3,367,809 2/1968 Soloff 72/56 M. Minchenko, Reynoldsburg; 3,483,611 12/1969 Balamuth el al..... 72/56 Frederick A. Desaw Columbus all 3,495,427 2/1970 Balamuth 72/56 or 01110 m] Asslgnee: ZZT,,Z,'{,3, 3;J"" ri/wr Eicmi tflli harc Herb Attorney cristopher B. Fragan, William D. Freeland [22] Filed: Mar. 8, 1971 et al.

[21] Appl. No; 122,215

Related US. Application Data [57] ABSTRACT [62] Division of Ser. No. 676,550, Oct. 19, 1967, Pat. No.

This invention relates generally to the application of 52 US. (:1 72 56, 29/243, 29/53 electromechanical transduccr gy to a wcrkpiccc. 51 Int. Cl B2lj /24 and particularly to thc utililaticn cf a high Q clcctrc- [58] Field 61 Search 72/56, DIG. mechanical trcnsduccr caPablc cf dclivcrins cmcmcly 29/243 5 high-power outputs to a work surface for thedeformation of metallic or non-metallic materials, such as, in 5 References Cited riveting, cold heading, bonding, and swaging.

UNITED STATES PATENTS 3,201,967 8/1965 Balamuth et a1 72/56 4 Claims, 7 Drawing Figures IO l5 l7 A A I9 PAIENIED SHEU 1 (IF 3 li/Am 1 METAL WORKING APPARATUS AND PROCESS This is a division of application Ser. No. 676,550, filed Oct. 19, 1967, for Metal Working Apparatus and Process," by Robert C. McMaster, et al now U.S. Pat. No. 3,609,851.

BACKGROUND An electromechanical transducer such as a piezoelectric device is capable of transforming high frequency electrical impulses into high frequency mechanical impulses or vice versa. With an alternatingpolarity input-voltage imposed on the piezoelectric elements, the transducer generates, transmits and amplifies a series of mechanical compression waves in the piezoelectric material and its metal supporting structure respectively. Considering the transducer alone, a succession of identical compression and tension waves transmitted in a transducer of proper length, produces a standing wave pattern.

In a straight bar the standing wave maxima and minima locations correspond respectively to locations of maximum and minimum velocity, minimum and maximum stress, and maximum and minimum displacement on the transducer body. These locations determine optimum positions for points-of-support, steps or changes in diameter, tools or mechanical couplers, etc. The node locations on the transducer correspond to'locations of minimum axial displacement and velocity, the anti-node locations correspond to locations of maximum axial displacement and velocity or motion. The distance measured on the trandsucer between adjacent anti-nodes is equal to one-half wavelength at the fundamental resonance frequency, the length being dependent and variable with the shape.

There is disclosed in the copending application filed by Robert C. McMaster and Berndt B. Dettloff on Nov. 19, I965, Ser. No. 508,815, for Fransducer, and assigned to The Ohio State University, a sonic transducer that combines the driving element (piezoelectric) with the mechanical displacement amplifier (horn) in a novel way. It is, in essence, a resonant horn structure excited internally close to the vibrational node. The excitation is in contrast to the external excitation com mon when horns are utilized in a sonic trandsucer system. The transducer therein disclosed in a high Q transducer, exceptionally rugged, compact, and capable of carrying continuous work loads.

There is disclosed in another copending application, also filed on Nov. 19, I965, Ser. No. 508,774, for Sonic Transducer" in the name of Charles C. Libby, and assigned to the same Assignee as the abovementioned application and the instant application, utilizing the principles of.the transducer in the aforementioned copending application. The over-all structure is improved and operable in a manner to demonstrate commercial feasibility. Some of the features of that transducer include a means of positioning or applying external force through a holding fixture supported near the node of the transducer. The clamping arrangement providing internal static stress or mechanical-bias is acoustically an integral part of the horn. The output end of the transducer is threaded for coupling an attachment to the tool. Other features are disclosed.

The use of sonic energy has been suggested extensively in all fields of endeavor. Although the use of sonic energy has been at an increasing pace, realistically its use has been limited by one primary factor, i.c.,

lack of sufficient power. The prior art, in referring to high-power transducers, refers to transudcers up to 10 watts.There is disclosed in the copending application filed on Aug. 10, 1966, Ser. No. 571,490, by Hildegard M. Minchenko for Electromechanical Transducer," Assignee, The Ohio State University, a transducer capable of delivering extremely high power, i.c., measurable in horsepower (or kilowatts) at an acoustical frequency range. The principle underlying the high-power output is in the structural arrangement of the components immediately associated with the piezoelectric driving elements. In theory and practice, the piezoelectric elements are under radial and axial pressure. In this way the piezoelectric elements are relieved of tension in operation even under intense sonic action. Significantly, the structural design that permits the extraordinary power output from the driving elements, resides in the novel method of clamping the piezoelectric elements both radially and longitudinally (axially). In this way the acoustic stresses in the piezoelectric elements are always compressive, never tensile, even under maximum voltage excitation.

There is further disclosed in the copending application filed on Dec. 28, 1966, Ser. No. 605,284, by Robert C. McMaster, Charles C. Libby and I-Iildegard M. Minchenko for Sonic Transducer Apparatus, and assigned to The Ohio State University, the means for efficiently coupling a highpower, high Q electromechanical transducer to drive a tool effectively, i.c., to drive the tool in a work environment. The significant feature of the invention is that the tool does not form a part of the resonant structure.

BRIEF DESCRIPTION OF THE INVENTION The present invention utilizes the aforementioned high Q electromechanical transducer and the aforementioned electromechanical transducer apparatus in a work environment. Specifically, a method and means has been achieved for sonically driving a metallic element until it is deformed. In the deformation of the metallic element, dynamic forces are substituted for the static forces of a conventional process. That is, the metallic element is deformed by dynamic forces with only a minimum amount of static pressure. The method comprises, basically, the utilization of high-power electromechanical energy to flow the metallic element. The means of the invention comprises the apparatus in a system configuration including the aforementioned transducer and the aforementioned transducer apparatus, together with the support structure and other attendant necessary components.

The utility of the present invention principally resides in joining two metallic or non-metallic sheets with rivets; forming heads on the rivets; or alternatively the energy may be utilized to enlarge the body of the rivet to maintain a force-fit in a preformed hole. Further, the principals of the present invention are equally applicable to other metal forming processes such as swaging", i.c., decreasing diameter or changing shape of the workpiece with the use of dies by series of hammer blows, or to cold heading, i.c., the use of dies and force to cause material to shorten and increase in diameter to fit a die.

It is accordingly a principal object of the present invention to provide method and means of utilizing highpower electromechanical energy in a metal forming work environment.

It is a further object of the present invention to provide method and means of utilizing high-power electromechanical energy to join or bind metallic or nonmetallic plates to one another with metal inserts or in other metal forming processes wherein the workpiece shape or size is altered.

It is another object of the present invention to provide. method and means of utilizing high frequency electromechanical energy in a metal forming process to substitute dynamic forces for static forces.

Other objects and fearures of the present invention will become apparent from the following detailed description when taken in conjunction with the srawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of the electromechanical transducer in the work environment;

FIG. 2 is an over-all schematic illustration of the high-power electromechanical transducer in the work environment;

FIG. 3 is an alternative arrangement illustrating the use of oppositely positioned electromechanical transducers;

FIG. 4 and 4a are other alternative arrangements illustrating different tool apparatus for use in metal deformation;

FIG. 5 is a schematic illustration of the complete system utilized in the bonding of two sheets of metal with metal inserts; and,

FIG. 6 is a graphical illustration of the frequency curves of the transducer va the impact frequency.

THEORY OF OPERATION The transducer in operation drives an impact tool which impact tool, in turn, deforms or changes the shape of the metallic member in a useful way. In specific embodiments this may be riveting, i.e., the formation of a. head on a metallic insert; swaging, i.e., decreasing the diameter or changing the shape of a workpiece; cold-heading, i.e., shortening or increasing the diameter of the workpiece; or other metallic deformation processes. In each process, through the utilization of the power-sonci energy, a dynamic force replaces the static force that is characteristic of the other forms of energy normally used in these metal working processes. Morespecifically, in the preferred embodiment of the present invention, the constant static force applied to the workpiece is drastically lessened or more specifically static force is not actually utilized in the metal working operation. The work effort in the deformation of the metallic member undergoing deformation is a dynamic force cyclically applied.

It is appreciated that ultrasonic energy has been utilized by the prior art in various metal working processes for instance in bonding. In the prior art bonding processes, the faying surfaces are rubbed together. Significantly, in this prior art process, there is little or no transfer of material from one surface to an other. The bonding occurs only in those areas of intimate contact. In the present invention, through the utilization of power-ultrasonic energy, when welding occurs there is actually a transfer of material of one surface to another. The faying surface are moved relative to each other but in contradistinction to the prior art there is an intermingling of the material between the two surfaces. Again it is stated, the primary significant difference between the present invention and that of the prior art in accomplishing the intended result is the availability (through the aforementioned transducer) of substantially increased amounts of power at the horm surface.

The exact nature of the joining or bonding of the hard merals is not fully appreciated and presently cannot be properly categorized in terminology relative to what occurs. In other types of metals such as aluminum, the type of bond is similar in appearance at the interface to that of explisive bonding. Again from cross-sectional analysis of riveted structure it does appear in some cases as though there is a weld between the rivet and the two plates. It can be appreciated, of course, that through the utilization of a dynamic force on the workpiece and consequently with the reduction of static force by a factor of I00 or more, the size of the structure, i.e., the machinery performing the work, is drastically reduced in size and cost. As a further illustration, with a single stroke static force or the mechanically vibratory metal deformation processes the hard metals, such as titanium, do not lend themselves to metal deformation processes such as riveting. In the instant invention, the dynamic force applied to the workpiece from the ultrasonic transducer can be understood as causing incremental deformation of the workpiece. The process of the present invention has been successful in the deformation of hard metals such as titanium without cracks in the junction and without creating a crystalline structure.

With reference to FIG. 6 it is seen that the frequency f, of the transducer motion and the frequency f, for the impact tool are not the same. Further, through the utilization of a resonant structure, the frequency f", of the transducer will be relatively constant, whereas the frequency of the impact tool,f,, changes increasing as the deformation decreases. Other factors to be taken in consideration in determining the frequency of the impact tool are the shape or dimensions of the dies, the work surface material, the static force applied, and the tool mass.

When operable in a metal deformation process the ultrasonic energy is applied to the workpiece or work surfaceby driving the rigid tool downward through impact with the transducer. The tool, in turn, impacts the metallic member to plastically deform the same in the desired manner. In theory the frequency differential between the transducer and the tool permits energy to be stored in the transducer between strokes of the tool. It is the utilization of this stored energy that develops the work force applied to the workpiece.

Again, with reference to FIG. 6, it is seen that in addition to the differential between the impact tooland transducer frequency there is an amplitude differential. Due to the high efficiency of the energy conversion from transducer motion to work deformation, the products of frequency and amplitude are approximately the same for the transducer and the tool. Thus, for example, a 10,000 cycle per second motion of 0.003 inch in a transducer may be converted to a 1,000 cycle per sec- 0nd 0.03 inch motion of the tool, or to a 3,000 cycle per second 0.01 inch motion of the tool depending on the factors described prieviously.

Spring back is a relatively constant force (for and given material) which accelerates the tool away from the deformed surface. The force is developed when the energy delivered to the work surface by ghe tool has been reduced sufficiently that the force required to continue plastic deformation can no longer be delivered by the tool. This occures when the stored energy of tool velocity (kinetic energy) is dissipated.

It is to be noted that the initial impact of the tool with the work surface causes the greatest deformation and with each succeeding impact less deformation occurs. The time required for deformation is reduced accordingly and spring back occurs at a more rapid pace with each succeeding impact. Thus a higher frequency of impact will occur as the deformation per stroke is reduced.

Gravity is not utilized in this cyclic process, that is, none of the steps described are dependent on gravity.

In producing the high dynamic forces (Force F) necessary to exceed the elastic-limit of the material used for the rivet, the riveting tool (Mass M) is decelerated (asseleration A) during the time of contact of the tool with the rivet. The equation F MA describes these dynamic inter-relationships.

Since it is also true that for every action there is an equal and opposite reaction, the rivet is simultaneously accelerated away from the tool-rivet inter-face with a force (F) approximately equal to the force generated by the tool impact.

In order to retain the rivet in location, or to minimize its total displacement away from the tool interface during impact, the inertia of the rivet system is increased by a back-up tool (in the embodiment of FIG. 1 holding device 45). This device, retained in position by a retaining or static force, is accelerated away from the rivet (rear side) by the force F, at the instanct of impact and tool deceleration. The same equation that relates the tool mass and its deceleration, relates the back-up mass and its acceleration.

Actually the retaining force slightly reduces the dynamic force available for acceleration of the'back-up tool during the impact. However, since the dynamic force is high enough to clastically deform the rivet material, and the retaining force is less than 400 pounds, the effect is minimal in the embodiment described.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now specifically to FIG. 1, there is shown in cross-section an electrical mechanical transducerutilized with the transducer apparatus in the joining of two sheets of meral with a metal insert. Specifically, transducer had coupled thereto an impact tool 20. As described in the aforementioned copending application, (Ser. No. 605,284), the impact tool 20 is positioned in free motion with the transducer 10 by the positioning means 15. Positioning means receiving slot 17, formed in the underside of the tip of transducer 10 and receiving slot 19 formed in the upper end of the impact tool 20 retain the positioning means in place. The impact tool also has formed in the underside thereof a cup-shaped depression 25. The size and contour of this depression may conform to that of a standard rivet head. Plates and are the work pieces which are intended to be joined together by the metallic insert specifically a rivet. The plates 30 and 35 are fixedly positioned to permit the rivet 40 to be directly in line with the receiving aperture 33 formed therethrough to receive rivets. The upper portion of the aperture 33 is countersunk, as shown at 37, to receive the metal flow.

Immediately beneath the plates 30 and 35 is a holding device 45. This device may be cylindrical in shape and is bored at 47 to receive the rivet extension 40a. On the underside of holding device 45 is a second cupshaped depression 43. Finally, the entire rivet forming structure is positioned in the non-movable base plate 50. The base 50 having a recess therein at 53 adapted to receive the holding device 45 and to retain the same in position.

In operation of the arrangement shown in FIG. 1, electromechanical energy is applied to the metal insert 40 by the downward force of the impact tool 20. The impact forces the metal insert 40 downward until its extreme end 40a abutts against the recess 47 in the hold-- ing device 45. With continued impact the metal rivet deforms until a rivet head is formed between the countersink 37 and the depression 25.

In the next step the plate assembly is reversed and the holding device 45 is inverted in order that the cupshaped depression 43 will receive the rivet head form ed by cup-shaped depression 25. With impact again applied, the previously formed rivet head seats itself in the depression 43 and the metal rivet deforms on its opposite end until a second rivet head is formed by the depression 25.

In an alternate arrangement a pair of transducers may be utilized in a manner as that shown in FIG. 3 to form a head at either end simultaneously from a straight shank rivet.

In other instances a preformed headed rivet may be utilized. With this arrangement, the holding device 43 will have its depression 43 in the upper position to receive the head of the rivet and the second step abovedescribed will be followed.

Referring now to FIG. 2 there is illustrated a highpower high Q transducer such as that described in the aforementioned copending application. This transducer has fixedly positioned thereon a transmission line 12 in direct alignment with the worktool 13 and workpiece 31. The straight shank rivets utilized had a length diameter of approximately 3 to 1.

Since alignment is important to the formation of a good rivet head, the impact tool 20 and holding device 25 in operation should be aligned properly; otherwise, the rivet will tip one way or the other and the head will be formed improperly.

With reference to FIG. 4 and 4a there is a first alternative arrangement of the work too] intended to accomplish the intended result of metallic deformation. In this embodiment the cup-shaped member 61 has its bottom area 63 as the driving member, i.e., the contact member between the tool and the deformable element.

In order that the method may be carried out with repetitive accuracy, the system illustrated schematically in FIGQS was developed. As pointed out above, the preferred embodiment included the high-power, high Q transducer 10, such as that disclosed in the aforementioned copending applications.

Specifically, the system structure 60 comprises supporting post 62 having a large foot plate 76 for maintaining the over-all structure in a steady state. A first cross-supporting member 64 has the vertical rotating mechanism incorporated therein to effect vertical movement of the driving post 66. To maintain vertical alignment of the transducer 10 is a second horizontal cross-supporting member 72; and to assure that the transmission line is in vertical alignment with the transducer 10, there is further provided supporting structure 70. The corss-member 72 has an aperture formed therein in direct vertical alignment with the driving post 66. Positioned at the end of driving post 66 and in alignment with the aperture in the member 72, is the transducer 10. It is, of course, understood that the coupling arrangement between the driving post 66 and transducer 10 can be varied. Positioned directly beneath the aperture in member 72 is the supporting structure 70. This structure 70 also has an aligned aperture formed in the base thereof. The baseis supported by rigid engagement with the member 72. The aperture in the base of the structure 70 is adapted to receive and position the transmission line 12.

Directly beneath and again in alignment the transmission line 12 is the structure 45 50 identical to that shown in FIG. 1.

Attached to the one lever arm 52 is the weight 68 for applying pressure to the transducer downward movement by the driving post 66. Also for convenience and accuracy, a pressure gauge may be attached to the lever to record the downward force.

In a specific preferred embodiment there was utilized a 50-kw motor generator operating at approximately 10,054 cycles per second. The transmission line 12 approximated 10.12 inches in length. The static forces applied to the impact tool are in the order of 450 pounds for rivets formed from straight shank rivets (/16 inch aluminum) having average shear strength of 3,000 to 3,400 pounds.

The good smooth uncracked surfaces indicated the yield strength of aluminum was exceeded. If static force alone were responsible for metal deformation then about 50 times the static force utilized here was required. In other words, with the use of ultrasonic energy a high dynamic force was used with a corresponding reduction of the required static force. The total elapsed time to form the rivet was one second or less per side with manual operation.

In reviewing the chronology of the actions in a rivet ing sequence, let us examine one series of action which is repeated thousands of times during a typical 1- second riveting action:

1. The tool impacts the driving transducer, and the tool is accelerated by the impact in the direction of the rivet. It stores kinetic energy as it picks up velocity.

2. The tool impacts the rivet-head and the tool mass M begins to decelerate, delivering kinetic energy to the tool-rivet interface.

3. The force F generated by the tool deceleration A is equal and opposite to the force accelerating the rivet away from the tool-rivet interface during this impact.

4. The product of mass of the tool M and its deceleration A, is numerically equal to the product of the mass (m) of the rivet (plus rest of the back-up mass-system). and the acceleration (a of that system during the time of rivet deformation, Thus F- M A mu.

5. The amplitude of the acceleration of the rivet away from the impact, is minimized by increasing the amplitude of the mass of the back-up mass system. This in turn reduces the total displacement of the rivet and the bending of theplate during rivet deformation.

6. The force (static force) retaining the back-up mass against the rear side of the plates, slightly reduces the dynamic force available for acceleration of the rivetmass system. Numerically this is a minimum reduction since the retaining force is only a few hundred pounds for inch rivets and the dynamic force is sufficient to plastically deform the rivet material.

7. The back-up mass or back-up inertia finally moved free of the rear of the rivet-mass system, and is restrained in its flight by only the retaining force or static force. This force acts in such a direction as to return the mass to its original position. The amplitude of the retaining force must be suffieient to return the back-up mass before the next successive stroke of the tool against the rivets.

8. The deceleration of the tool (and its dissipation of stored kinetic ene gy) Continues, as long as the rate at which the tool can deliver energy (or as ong as the force developed by deceleration) is sufficient to maintain the rivet in plastic deformation.

9. When the tool ceases to decelerate at sufficient rate to maintain the rivet material in a plastic state, the rivet material freezes" or springs-back" to its solid, non-plastic state.

10. This spring-back action accelerates the tool in the direction of the tool interface and away from the rivet interface. It also accelerates the rivet-back-up mass system away from the rivet interface, in an opposite direction, with an equal force. This spring-back force accelerating the rivet and back-up mass away from the rivet interface, is in the same direction, and is a continuation of, the force described in (3).

ll. The cycle is now completed, with all dynamic driving and working forces and static restraining forces having been described.

Although certain and specific embodiments have been illustrated, it is to be understood that modification may be made without departing from the true spirit and scope of the invention.

What is claimed is: g

1. The method of deforming a metallic member including an energy storage system and a tool mass comprising:

a. extracting said stored energy at time rate enormously greater than the time rate of sid energy stored;

b. utilizing said exhausted energy for accelerating said mass to a high velocity thereby converting said stored energy into motional energy, i.e., kinetic energy of said tool mass;

0. positioning a deformable work surface in the path of said tool motion thereby causing said tool to impact said work surface;

d. aligning said storage energy system and said mass,

said impact completely decelerating said tool motion, the work on said work surface being equivalent to said kinetic energy stored in said tool mass, and

wherein said work equals the product of the dynamic force developed during deceleration and distance in deceleration occurs;

e. cyclincally applying a reaction mass against said work surface with an external force equal to the force which accelerates the reaction mass away from the back side of the work surface.

2. The method of claim 1 wherein the cycle is repeated thereby totally deforming said metallic material in a series of incremental steps.

3. The method of claim 2 further comprising the step of statically retaining and returning to position said reaction mass in a time equal to or less than the time between repetitious of the said cycle.

4. The method of claim 1 wherein the step of externally retaining comprises statically forcing in an order of magnitude less than the dynamic force necessary to cause metal deformation of the work surface area.

l *i l ll 

1. The method of deforming a metallic member including an energy storage system and a tool mass comprising: a. extracting said stored energy at time rate enormously greater than the time rate of sid energy stored; b. utilizing said exhausted energy for accelerating said mass to a high velocity thereby converting said stored energy into motional energy, i.e., kinetic energy of said tool mass; c. positioning a deformable work surface in the path of said tool motion thereby causing said tool to impact said work surface; d. aligning said storage energy system and said mass, said impact completely decelerating said tool motion, the Work on said work surface being equivalent to said kinetic energy stored in said tool mass, and wherein said work equals the product of the dynamic force developed during deceleration and distance in deceleration occurs; e. cyclincally applying a reaction mass against said work surface with an external force equal to the force which accelerates the reaction mass away from the back side of the work surface.
 2. The method of claim 1 wherein the cycle is repeated thereby totally deforming said metallic material in a series of incremental steps.
 3. The method of claim 2 further comprising the step of statically retaining and returning to position said reaction mass in a time equal to or less than the time between repetitious of the said cycle.
 4. The method of claim 1 wherein the step of externally retaining comprises statically forcing in an order of magnitude less than the dynamic force necessary to cause metal deformation of the work surface area. 